In forming a wiring of a semiconductor integrated circuit, there is included a process of forming, e.g., a contact hole or a groove for wiring. In such a process, a resist film layer and an anti-reflection coating film layer are formed on an insulating film layer made of, e.g., silicon oxide, and, further, a pattern for the contact hole or the groove is formed thereon by using a photolithography technique, after which an etching is performed by using a plasma processing apparatus according to the pattern, to thereby form the contact hole or the groove. Next, an ashing is carried out by using the same or a different plasma processing apparatus to remove the resist film layer.
FIGS. 5A and 5B describe a conventional ashing process. There is shown in FIG. 5A a structure having, starting from top to bottom, a photoresist film layer (PR film layer) 102, an anti-reflection film layer [BARC (bottom anti-reflection coating) layer] 103, a silicon oxide film layer (SiO2 film layer) 104 and a silicon oxy nitride film layer (SiON film layer) 105 formed on a silicon layer 101 of a wafer. The SiO2 film layer 104 and the SiON film layer 105 incorporate a contact hole 106 formed by etching. In ashing the PR film layer 102 shown in FIG. 5A, the PR film layer 102 along with the BARC layer 103 formed on the SiO2 film layer 104, is removed thereby. For such conventional processing, a chamber made of, e.g., alumite-treated aluminum or alumina, is used as a vacuum processing vessel of the plasma processing apparatus.
In executing such processing, there is a problem of contaminant generation due to damages on chamber material by the plasma incurring with age. In particular, in a case of the chamber being made of aluminum or a material containing aluminum such as alumina, the etching performed by using a fluorine-based gas results in a generation of particles such as aluminum fluoride. To solve such problem, recently a chamber having an inner surface thereof thermally sprayed with ceramic such as yttria (Y2O3) has been employed to improve plasma resistance, which in turn stretches a periodic cleaning cycle of the chamber.
In a case of such chamber being treated with the ceramic thermal spray, e.g., a yttria thermal spray, the etching is performed by using a predetermined etching gas to form the contact hole 106 at the SiO2 film layer 104, as shown in FIG. 5A, and, subsequently, the ashing is executed by using, e.g., an O2 gas, at a predetermined pressure of, e.g., 200 mTorr, to thereby remove the PR film layer 102, as shown in FIG. 5B. In this case, however, crater-shaped holes 107 (hereinafter, referred to as craters for simplicity) formed by an abnormal etching are found at a surface of the SiO2 film layer 104, particularly, around the contact hole 106.